Means of preventing embrittlement in metals exposed to aqueous electrolytes



United States Patent 3,1tl9,7 34 MEANS OF PREVENTENG EMBRITTLEMENT IN METALS EXPOSED T0 AQUEGUS ELEC- TRGLYTES Claude R. Bishop, Niagara Falls, and Milton Stern, Tonawanda, N.Y., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Feb. 18, 1959, Ser. No. 793,960 5 Claims. (6!. 75-174) This invention relates to the prevention of hydrogen embrittlement in metals, and particularly, to the prevention of hydrogen embrittlement resulting from electrochemical action. I

The embrittlement of certain metals by absorbed hydrogen is generally related to chemical and electrochemical corrosion processes. But unlike those forms of corrosive attack of an environment on a metal, the hydrogen embrittlement of a metal does not necessarily result in the destruction of the metal by chemical reactions with oxidants, but rather the metal undergoes a loss of ductility, or embrittlement, which often results in failure. The types of failure are broad, ranging in nature from extreme brittleness to surface blistering. It is believed to be the diffusion of atomic hydrogen into the metal that produces this embrittling effect.

The environments causing embrittlement vary, depending on the metal and whether or not the environment supports the production of atomic hydrogen. The electrochemical corrosion processes taking place on the surface of a metal may cause the formation of atomic hydrogen. This is particularly so in the case of acid electrolytes. Precautions taken to protect a metal surface from the oxidative effects of electrochemical corrosion will not necessarily protect the metal from hydrogen embrittlement, and, may in fact accelerate the attack. Again metals subjected to cathodic charging during electrolysis may be subjected to the action of atomic hydrogen.

Many metals are affected by hydrogen embrittlement. Failure from this condition has been reported for tantalum, and tantalum-titanium alloys, as well as for the straight chromium stainless steels. Some grades of carbon steel are also effected by the presence of hydrogen. Blistering is a common defect encountered on steels. exposed to environments in which atomic hydrogen is liberated.

The rate of penetration of hydrogen is generally governed by the concentration of hydrogen on the surface of the metal. The presence of residual stresses, such as those resulting from cold working seems to accelerate the rate of absorption.

Many attempts have been made to overcome this difficulty, such as by controlling the purity of the metal and the use of special heat treatments, but no effective solution to the problem has been found.

It is the primary object of this invention, therefore, to provide means for preventing embrittlement in metals exposed to aqueous electrolytes.

It is a further object of this invention to provide alloys that are resistant to hydrogen embrittlement.

Other aims and advantages of this invention will be apparent from the following description and the appended claims.

In accordance with the present invention these objects are provided by alloying with tantalum, tantalum-titanium alloys, and stainless steels at least one metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, rhenium, and alloys thereof.

The noble metals listed above may be considered the low-hydrogen, overvoltage group of metals. The mechanism by which the low-hydrogen, overvoltage metals are "ice immunized to hydrogen-induced embrittlement is believed to be due to their ability to attract atomic hydrogen. The atomic hydrogen thus accumulates on the low-hydrogen, overvoltage metal rather than over the surface of the host metal or alloy. Whereas the presence of atomic hydrogen on the surface of the host metal would result in the diffusion of the hydrogen into the host metal, the accumulation of atomic hydrogen on the low-hydrogen, overvoltage metal merely results in the combination of the atomic hydrogen whereby molecular hydrogen is liberated. Hydrogen in the molecular state does not easily enter the host metal.

Example 1 This cold rolled specimen was etched in hydro-fluoric acid to ensure the presence of a fresh surface. When tested under conditions of cathodic charging at 10 ma./crn. current density in an electrolyte for one hour, the specimen showed no cracks after a bend test. Thus the small amount of noble metal added was effective in preventing embrittlement. In similar tests performed on unalloyed tantalum under conditions of cathodic charging, the specimens cracked in bend tests after an hour or an hour and a half.

Example 2 Alloys composed of tantalum and up to about 50 percent titanium are also susceptible to embrittlement in certain media. Under conditions of cathodic charging this embrittlement is accelerated. An alloy was prepared consisting of 40 percent by weight titanium, 0.5 percent by weight platinum, and the balance tantalum. A specimen was prepared, annealed and etched in hydrofluoric acid to ensure the presence of a fresh surface. When tested under conditions of cathodic charging at 20 ma./cm. for 7 hours, the specimen showed no cracks after a bend test.

Example 3 The embrittling of the chromium stainless steels due to hydrogen absorption has also been reported. To show the beneficial effects of noble metal alloying on type 410 stainless steels, a specimen of type 410 stainless steel containing 0.4 percent by weight platinum was subjected to an embrittling environment of 10 percent hydrochloric acid plus 2 percent selenium dioxide. The specimen tested had a hardness corresponding to a Rockwell C test reading of 40. The specimen was stressed by being fastened to a spring type holder while immersed in the acid environment. While a stainless steel specimen containing 0.4 percent platinum was able to withstand embrittling environment for up to 24 hours, other stainless steel specimens unprotected by noble metal additions broke in only 3 /2 hours under similar conditions. Among other chromium stainless steels made resistant by this process to hydrogen embrittlement are Types 304 and 316.

Since very small amounts of noble metal additions are effective in providing hydrogen embrittlement resistance, amounts of noble metals as low as 0.05 percent by weight may be alloyed with the susceptible metals to provide hydrogen resistance in dilute environments. Again additions up to and over 1 percent by weight may be utilized. Additions above 5 percent by weight do not in general not necessarily to constitute a limitation upon the scope of the invention.

What is claimed is: 1. An alloy characterized by resistance to hydrogeninduced embrittlement in aqueous electrolytes, said alloy consisting essentially of about 0.5 percent by Weight in the aggregate of at least one metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, rhenium, and mixtures thereof, and the balance tantalum and incidental impunities.

2. An alloy characterized by resistance to hydrogeninduced embrittlement in aqueous electrolytes, said alloy 7 consisting essentially of about 0.5 percent by Weight platinum, and the balance tantalum and incidental impurities.

3. An alloy characterized by resistance to hydrogeninduced embrittlement in aqueous electrolytes, said alloy consisting essentially of about 0.5 percent by weight in the aggregate of at least one metal selected from the 3 group consisting of ruthenium, rhodium, palladium, os-

mium, iridium, platinum, gold, rhenium, and mixtures 4 thereof, at least 50 percent by weight tantalum, and the balance titanium, and incidental impurities.

4. An alloy characterized by resistance to hydrogen induced embrittlement in aqueous electrolytes, said alloy consisting essentially of about 0.5 percent by Weight platinum, at least 50 percent by weight tantalum, and the balance titanium, and incidental impurities.

5. A hydrogen-embritvlement resistant alloy consisting essentially of from about 0.05 to about 5 percent by weight of at least one metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, rhenium, and mixtures thereof, at least 50 percent by weight tantalum, and the balance titanium, and incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS 1,167,827 Kaiser Jan. 11 1916 1,742,417 Schrobsdorfi Jan. 7, 1930 1,809,436 Carman June 9, 1931 1,809,437 Carman June 9, 1931 FOREIGN PATENTS 18,212 Great Britain July 9, 1914 of 1913 517,362 France Dec. 17, 1920 OTHER REFERENCES The Book of Stainless Steels, 2nd Ed, 1935, page 8. Edited by E. E. Thum and published by The American Society for Metals, Cleveland, Ohio. 

5. A HYDROGEN-EMBRITTLEMENT RESISTANT ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 0.05 TO ABOUT 5 PERCENT BY WEIGHT OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF RUTHENIUM, RHODIUM, PALLADIUM, OSMIUM, IRIDIUM, PLATINUM, GOLD, RHENIUM, AND MIXTURES THEREOF, AT LEAST 50 PERCENT BY WEIGHT TANTALUM, AND THE BALANCE TITANIUM, AND INCIDENTAL IMPURITIES. 